Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.56   5.858%   $25.9987   $26.00   $26.00   $26.00  
  Purchase #2 $187.33   6.249%   $199.0363   $199.04   $199.05   $199.00  
  Purchase #3 $190.81   11.464%   $212.6845   $212.68   $212.70   $212.70  
  Purchase #4 $76.85   12.840%   $86.7175   $86.72   $86.70   $86.70  
  Purchase #5 $62.73   11.735%   $70.0914   $70.09   $70.10   $70.10  
  Purchase #6 $188.33   4.320%   $196.4659   $196.47   $196.45   $196.50  
  Purchase #7 $162.37   3.618%   $168.2445   $168.24   $168.25   $168.20  
  7 purchase totals = $892.98       $959.2388   $959.24   $959.25   $959.20